M3 Headphone Amplifier - Take Two

Background

Some time ago, a fellow head-fi'er put up a not-quite-finished M3 for sale and his add caught my attention. I had spoken with him in the past and seemed to remember that the M3 was a dream of his. It seemed he had done all the soldering, but that the casework had effectively stopped his project from being finalized. I contacted him and suggested that instead of selling the project (I already have an M3) we should build a proper case for it so that he would be able to enjoy music the way he intended to. He quickly accepted and we started talking design.

Hard decisions

This is what I got, along with a box of stuff for the build. The build featured:

• M3 Amplifier from AMB Laboratories.
• Sigma11 Power Supply fromAMB Laboratories.
• Epsilon24 Power switch Driver Circuit from AMB Laboratories.
• Sigma24 Transformer Board from AMB Laboratories.
• Sigma25 Regulated Power Supply from AMB Laboratories.
• Epsilon12 Headphone Amp Muting delay & DC offset protection circuit from AMB Laboratories.

As you might gather, the original intention was to have a relay turn on the amp, we abandoned this idea. Also, he wanted to watch movies through this amp and I know from my Beta22
that the protection relay behaves quite erratic in the standard configuration and often triggers when I play PC games, so we abandoned that also. My own M3 does not have the protection relay either and I have never had a problem with it.

Sigma11

The Sigma11 was chosen as power supply as it complements the M3 design nicely.